Urolithiasis

Urolithiasis is a condition arising from the formation of renal calculi when the urine is supersaturated with salt and minerals such as calcium oxalate, struvite (ammonium magnesium phosphate), uric acid and cystine¹ . 80% of stones contain calcium² . These urinary tract stones vary considerably in size from small 'gravel-like' stones to large staghorn calculi. The calculi may stay in the position in which they are formed, or migrate down the urinary tract, producing symptoms along the way. Studies suggest that the initial factor involved in the formation of a urinary tract stone may be the presence of nanobacteria that form a calcium phosphate shell^{3 4} .

The other factor that leads to urolithiasis/urinary tract stone production is the formation of Randall's plaques. Calcium oxalate precipitates form in the basement membrane of the thin loops of Henle; these eventually accumulate in the subepithelial space of the renal papillae, leading to a Randall's plaque and eventually a calculus⁵ .

Bladder stones
Bladder stones (calculi) account for around 5% of urinary tract stones and usually occur because of foreign bodies, obstruction or infection⁶ . The most common cause of bladder stones is urinary stasis due to failure of emptying the bladder completely on urination, with the majority of cases occurring in men with bladder outflow obstruction⁷ . Approximately 5% of bladder stones occur in women and are usually associated with foreign bodies such as sutures, synthetic tapes or meshes, and urinary stasis, so bladder stones should always be considered in women investigated for irritable bladder symptoms or recurrent urinary tract infections⁸ .

Patients with indwelling Foley catheters are also at high risk for developing bladder stones and there appears to be a significant association between bladder stones and the formation of malignant bladder tumours in these patients.

Epidemiology²

• Urinary tract stones, particularly renal stones, are common, being present at some time in one in ten of the population, although a significant proportion will remain asymptomatic.

• The annual incidence is about 1-2 cases of acute renal colic (or ureteric colic) per 1,000 people and the average lifetime risk around 5-10%.

• Men are more commonly affected than women, with a male:female ratio of 3:1. The difference between the sexes is gradually being eroded. This is thought to be due to lifestyle-associated factors, such as obesity and a Western diet.

• Urinary stones occur mainly in white people, followed by Hispanics, black people, and Asians.

• The peak age for developing urinary tract stones is 40-60 years for men and in the late 20s for women.

Risk factors

Several risk factors are recognised to increase the potential of a susceptible individual to develop urinary tract stones or urolithiasis. These include:

• Anatomical anomalies in the kidneys and/or urinary tract - eg, horseshoe kidney, ureteral stricture.

• Family history of urinary tract stones. Stone formation is twice as likely to occur in people who have a first-degree relative with stones.

• Hypertension.

• Gout.

• Hyperparathyroidism.

• Immobilisation.

• Relative dehydration.

• Metabolic disorders which increase excretion of solutes - eg, chronic metabolic acidosis, hypercalciuria, hyperuricosuria.

• Chronic lead and cadmium exposure are associated with stone formation.

• Deficiency of citrate in the urine.

• Cystinuria (an autosomal-recessive aminoaciduria).

• Drugs - eg, diuretics such as triamterene and calcium/vitamin D supplements.

• More common occurrence in hot climates, due to the effect on fluid status and urine volume.

• A diet with excessive intake of oxalate, urate, sodium, and animal protein.

• Increased risk of stones in higher socio-economic groups.

• Obesity - the association seems to be greater in women than in men. It is thought that low urine pH and uric acid stones and an association with hypercalciuria could account for an increased risk of uric acid and/or calcium stones in obese people.

• Contamination - as demonstrated by a spate of melamine-contaminated infant milk formula⁹ .

• Risks for recurrent stone formation include:

  • Type of stone - people with calcium-containing stones, uric acid and ammonium urate stones, and infection stones (such as struvite stones).

  • Positive family history of stones.

  • Previous stone formation.

  • Early onset of stones.

Presentation²

• Many urinary tract stones are asymptomatic and discovered during investigations for other conditions.

• The classical features of renal colic are sudden severe pain. It is usually caused by stones in the kidney, renal pelvis or ureter, causing dilatation, stretching and spasm of the ureter. In most cases no cause is found:
  

  • Pain starts in the loin about the level of the costovertebral angle (but sometimes lower) and moves to the groin, with tenderness of the loin or renal angle, sometimes with haematuria.

  • If the stone is high and distends the renal capsule then pain will be in the flank but as it moves down pain will move anteriorly and down towards the groin.

  • A stone that is moving is often more painful than a stone that is static.

  • The pain radiates down to the testis, scrotum, labia or anterior thigh.

  • Whereas the pain of biliary or intestinal colic is intermittent, the pain of renal colic is more constant but there are often periods of relief or just a dull ache before it returns. The pain may change as the stone moves. The patient is often able to point to the place of maximal pain and this has a good correlation with the current site of the stone.

• Other symptoms which may be present include:

  • Rigors and fever.

  • Dysuria.

  • Haematuria.

  • Urinary retention.

  • Nausea and vomiting.

Examination

• The patient with colic of any sort writhes around in agony. This is in contrast to the patient with peritoneal irritation who lies still.

• The patient is apyrexial in uncomplicated renal colic (pyrexia suggests infection and the body temperature is usually very high with pyelonephritis).

• Examination of the abdomen can sometimes reveal tenderness over the affected loin. Bowel sounds may be reduced. This is common with any severe pain.

• There may be severe pain in the testis but the testis should not be tender.

• Blood pressure may be low.

• Full and thorough abdominal examination is essential to check for other possible diagnoses - eg, acute appendicitis, ectopic pregnancy, aortic aneurysm.

Differential diagnosis¹⁰

This depends upon the position of the pain and the presence or absence of pyrexia and includes:

• Biliary colic.

• Dissection of an aortic aneurysm: beware the patient who presents with features of renal colic for the first time over the age of 60 years. This may be dissection of aortic aneurysm leading to ruptured aortic aneurysm.

• Pyelonephritis: very high temperature. Pain is unlikely to radiate to the groin.

• Acute pancreatitis.

• Acute appendicitis.

• Perforated peptic ulcer.

• Epididymo-orchitis or torsion of the testis: very tender testis.

• Sinister causes of back pain: usually tender over vertebrae.

• Drug misuse: there are reports of people with fictitious stories of renal colic, designed to obtain an injection of pethidine. These patients tend to be abusive when offered anything other than pethidine.

• Münchhausen's syndrome¹¹ .

Investigations^{2 12}

• Basic analysis should include:
  

  • Stick testing of urine for red cells (suggestive of urolithiasis), white cells and nitrites (both suggestive of infection) and pH (pH above 7 suggests urea-splitting organisms such as Proteus spp. whilst a pH below 5 suggests uric acid stones).

  • Midstream specimen of urine for microscopy (pyuria suggests infection), culture and sensitivities.

  • Blood for FBC, CRP, renal function, electrolytes, calcium, phosphate and urate, creatinine.

  • Prothrombin time and international normalised ratio if intervention is planned.

• Urgent imaging (within 24 hours) should be offered to all people with suspected stones. Non-enhanced CT scanning is now the preferred imaging modality for most adults and has replaced intravenous pyelogram (IVP) .

• Ultrasound scanning should be offered to pregnant women, children and young adults.

• If renal colic is suspected in children and young people after a negative ultrasound scan, a low-dose non-enhanced CT scan should be considered.

• Guidelines from the National Institute for Health and Care Excellence (NICE) recommend stone analysis for adults with ureteric or renal stones.

• Encourage the patient to try to catch the stone for analysis. This may mean urinating through a tea strainer, a filter paper such as a coffee filter or a gauze.

• Consider referring children and young people with ureteric or renal stones to a paediatric nephrologist or paediatric urologist with expertise in this area for assessment and metabolic investigations.

Management^{2 12}

Initial management of urolithiasis or urinary tract stones can either be done as an inpatient or on an urgent outpatient basis, usually depending on how easily the pain can be controlled.

Indications for hospital admission

• Signs of systemic infection - eg, fever, sweats, sepsis.

• Increased risk of acute kidney injury - eg, solitary kidney, known non-functioning kidney, transplanted kidney, suspected bilateral renal stones.

• Inadequate pain relief or persistent pain.

• Inability to take adequate fluids due to nausea and vomiting.

• Anuria.

• Inability to arrange imaging within 24 hours.

• Diagnostic uncertainty.

For all other patients, offer urgent imaging (see Investigations, above).

Initial management of acute presentation

• Non-steroidal anti-inflammatory drugs (NSAIDs), usually in the form of diclofenac IM or PR, should be offered first-line for the relief of the severe pain of renal colic. NSAIDs are more effective than opioids for this indication and have less tendency to cause nausea. If NSAIDs are contra-indicated, offer IV paracetamol. If both are contra-indicated or are ineffective, consider opiates. A Cochrane review concluded that it should not be pethidine, which is more likely than other options are to induce vomiting¹³ .

• Provide antiemetics and rehydration therapy if needed.

• There is no place for antispasmodics.

• Further management depends on the size of the stone, the likelihood of spontaneous passage, whether the stone is renal or ureteric, the severity of symptoms, the patient's age, and any relevant contra-indications or comorbidities.

• Urgent imaging should take place within 24 hours as mentioned above, to confirm diagnosis, assess the likelihood of spontaneous passage, and identify anatomical or medical conditions likely to cause recurrence.

• Watchful waiting should be considered for asymptomatic renal stones in adults, children and young people if the stone is:

  • Less than 5 mm.

  • Larger than 5 mm and the person (or their family or carers, as appropriate) consents to watchful waiting after an informed discussion of the possible risks and benefits.

• Medical expulsive therapy may be used to facilitate the passage of the stone. It is considered in cases where the stone is located distally. The optimal size is greater than 5 mm but less than 10 mm in diameter. Alpha-blockers (eg, tamsulosin) are given¹⁴ .

Managing patients at home

• All patients managed at home should drink a lot of fluids and, if possible, void urine into a container or through a tea strainer or gauze to catch any identifiable calculus.

• Analgesia: paracetamol is safe and effective for mild-to-moderate pain; codeine can be added if more pain relief is required. Paracetamol and codeine should be prescribed separately so they can be individually titrated.

Surgical

• If the pain cannot be tolerated or the stone is unlikely to pass, surgical treatment should be considered for adults with ureteric stones and renal colic within 48 hours of diagnosis or readmission. The choice of procedure depends on such factors as the size of the stone, the person's age, contra-indications, a history of failed previous procedure, and anatomical considerations.

• Options include:

  • Extracorporeal shock wave lithotripsy (ESWL) - shock waves are directed over the stone to break it apart. The stone particles will then pass spontaneously.

  • Percutaneous nephrolithotomy (PCNL) - used for large stones (>2 cm), staghorn calculi and also cystine stones. Stones are removed at the time of the procedure using a nephroscope.

  • Ureteroscopy - this involves the use of laser to break up the stone and has an excellent success rate in experienced hands.

  • Open surgery - rarely necessary and usually reserved for complicated cases or for those in whom all the above have failed - eg, multiple stones.

• Several options are available for the treatment of bladder stones. The percutaneous approach has lower morbidity, with similar results to transurethral surgery while ESWL has the lowest rate of elimination of bladder stones and is reserved for patients at high surgical risk⁷ .
  

Complications²

• Complete blockage of the urinary flow from a kidney decreases glomerular filtration rate (GFR) and, if it persists for more than 48 hours, may cause irreversible renal damage.

• If ureteric stones cause symptoms after four weeks, there is a 20% risk of complications, including deterioration of renal function, sepsis and ureteric stricture.

• Infection can be life-threatening.

• Persisting obstruction predisposes to pyelonephritis and pyelonephrosis.

• A large study identified an association between kidney stones, renal cell carcinoma (RCC) and upper tract urothelial carcinoma (UTUC) in people aged 55-69 years¹⁵ .

• A possible link between coronary heart disease, stroke and renal stones has been detected.

• Occasionally, rupture of a renal calyx can occur, leading to the formation of a urinoma.

Prognosis²

• It has been calculated that 95% of ureteral stones up to 4 mm pass within 40 days.

• Stones between 5 mm and 10 mm in diameter pass spontaneously in about 50% of people.

• A systematic review found that¹⁶ :

  • 64% of people spontaneously passed their stones: approximately 49% of upper ureteral stones, 58% of mid-ureteral stones, and 68% of distal ureteral stones were successfully passed.

  • Almost 75% of stones less than 5 mm and 62% of stones 5 mm or more passed spontaneously.

  • It took about 17 days for stone expulsion to occur (range 6–29 days).

  • Nearly 5% of participants required re-admission to hospital because their condition had deteriorated.

• Recurrence in people who have not had previous stones is 50% at five years and 80% at 10 years.

Prevention²

Recurrence of urinary tract stones like renal stones or bladder stones is common and therefore patients who have had a renal stone should be advised to adapt and adopt several lifestyle measures which will help to prevent or delay recurrence:

• Increase fluid intake to maintain urine output at 2-3 litres per day.

• Add fresh lemon juice to drinking water and avoid carbonated drinks.

• Reduce salt intake.

• Eat a healthy diet and maintain a normal weight.

• Do not restrict calcium intake.

• Depending on the composition of the stone, medication to prevent further stone formation is sometimes given:

  • Consider potassium citrate for:
    

    • Children and young people with a recurrence of stones that are mainly (more than 50%) calcium oxalate, and with hypercalciuria or hypocitraturia.

    • Adults with recurrent stones that are mainly (more than 50%) calcium oxalate

  • Consider thiazide diuretics for adults with a recurrence of stones that are mainly (more than 50%) calcium oxalate and hypercalciuria, after restricting their sodium intake to no more than 6 g a day.